a) Field of the Invention
The present invention is concerned with a very simple yet efficient device that can be added to most of the commercially available residential air source heat pumps used to heat or cool a dwelling, a house or any similar building, in order to make it possible for such a heat pump to be used as a water heater for a swimming pool located nearby or inside the dwelling, house or building, without the heat pump loosing any of its primary function, i.e. heating and cooling of the dwelling, house or building.
b) Brief Description of the Prior Art
Swimming pool heating has been traditionally done by means of water heaters taking their energy from fossil fuels, electricity or solar panels.
Recently, it has been proposed to use heat pumps instead of gas, oil, electric or solar systems, in order to heat swimming pools. Heat pumps are well known devices which, in this particular application, use their refrigerant circuit to "pump" ambiant heat through an evaporator and transfer it to the swimming pool water through a condenser in which the water is circulated. An example of such a system making use of a heat pump to heat an indoor swimming pool while simultaneously dehumidifying the ambient air passing through the evaporator is disclosed in Canadian patent No. 1,221,838.
It has also been proposed to use refrigerating apparatus to heat pools or domestic water. Thus, by way of example, U.S. Pat. No. 3,976,123 discloses an air conditioning system including a heat exchanger in which the rejected energy is used to heat a swimming pool. Although the heat exchanger could be implemented as an add-on device, its positioning after the outdoor coil is such that even if the exterior fan is stopped, the system will be less efficient than if it would have been installed immediately after the compressor, as is proposed in accordance with the present invention.
It is also recognised that air conditioning cannot provide sufficient heat at the beginning and at the end of the pool heating season. As a result, supplemental heat from a heater or the house furnace is necessary when use is made of such a system. Furthermore, the system disclosed in this patent does not make use of a pressure regulated flow valve, or any other type of circuits to maintain the compressor head pressure when pool water is cold such that proper refrigeration cycle is insured, resulting in poor system performance and possible freezing of interior heat pump heat exchanger. In addition the system disclosed in this patent does not make use of a water flow sensing device. As a result, if the filter pump is stopped or if the filter is operated in backwash mode, this leads to high pressure at the compressor outlet and causes the system to stop.
U.S. Pat. No. 3,188,829 discloses a heat pump with a heat exchanger located between its compressor and its reversing valve to heat domestic hot water. The system disclosed in this patent has very specific control system which as substantially different from what is proposed in accordance with the present invention. In this U.S. Pat. No. 3,188,829, a bypass extands from the outlet of the compressor to the receiver with a check valve and a control valve. This circuit is of prime importance to the system since it maintains a predetermined minimum system pressure at the refrigerant storage means. However, it is structurally complicated and costly to implement as an "add-on a heat pump", because no commercially available heat pump is equipped with such a by-pass. Also in this patent, the control system does not stop the operation of the outside fan during cooling, reducing the amount of energy rejected to the pool. Furthermore, the control system does not permit to initiate heat pump operation if pool heating is required and if the heat pump is on stand-by. This feature would require that the inside fan be prevented from operating.
Finally in U.S. Pat. No. 3,188,829, a water by-pass and a diverting valve is provided to prevent circulation of water in the heat exchanger, in the defrosting mode. This is again different from what is proposed in accordance with the present invention, where a pressure regulated water flow valve is used, which automatically closes the water circuit if the heat pump is in the defrosting mode.
It has also been proposed so far to use swimming pools as heat sources from which heat can be extracted by a heat pump to heat buildings. Examples of such a system where the swimming pool water is circulated through the heat pump evaporator, are disclosed in French laid-open patent application Nos. 2,428,783 and 2,564,953.